In recent years, there has been an increasing demand for reliable and objective evaluation of sport specific data. The measurement and analysis of the trajectories of athletes is one possible approach to gain such insights. It allows the assessment of the physical performance and tactical behavior of athletes. Thus, it can yield helpful feedback for athletes, coaches and referees. Furthermore, spectators can be supplied with additional information about the accomplishments of their idols.
Local Positioning Systems provide a means for the measurement of athletes positions and motion trajectories. State-of-the-art systems use time-of-arrival or time-difference-of-arrival measurements of electromagnetic waves. These electromagnetic waves travel between base stations with fixed and known positions and mobile transponders with unknown and variable positions. When such a mobile transponder is attached to an object or person, the position of this object or person can be determined from the position of the mobile transponder.
Using the time measurements from several base stations with respect to the mobile transponder, the position of the mobile transponder in the coordinate system of the local positioning system can be determined. Although such systems can offer accurate position data under ideal measurement conditions, they often suffer from deficient behavior when used at a real sports venue.
One of the most relevant sources of positioning inaccuracies is the occurrence of multipath and non-line-of-sight (NLOS) errors. NLOS errors occur when the signal between a base station and a mobile transponder is not received via the direct path but via a reflection. This leads to an erroneous time measurement and thus to an erroneous calculated position. The magnitude of NLOS errors is theoretically unlimited. Multipath errors occur when NLOS signals interfere with the line-of-sight (LOS) signal which also leads to erroneous measurements.
To determine the position of a mobile transponder, measurements from several base stations are necessary. However if the measurement of only a single base station is corrupted by a NLOS or multipath error, considerable errors in the calculated position may occur.